A sheath inner heat and outer cold prestress elimination system and method based on PLC closed loop control

Abstract

The application relates to a sheath inner-heat outer-cool prestress elimination system and method based on PLC closed-loop control, which comprises: closed connection assemblies connected to the two ends of a sheath to be treated respectively, used for sealing the two ends of the sheath and providing interfaces for internal medium circulation; load bearing ropes arranged in the sheath and connected to the closed connection assemblies at two ends respectively and extended to the outside of the sheath, used for bearing axial tension; a high-temperature circulation module used for circulating and supplying heated liquid medium to the inside of the sheath, so that the inner wall of the sheath is heated to a preset temperature; a low-temperature spraying module comprising a spraying ring, which is sleeved on the outside of the sheath and used for spraying and cooling the outer wall of the sheath, so that the temperature of the outer wall of the sheath is lower than that of the inner wall, and a radial temperature difference is established in the thickness direction of the sheath wall; and a servo tension module. The application can eliminate the residual prestress generated in the forming and coiled storage process of a polyurethane sheath.

Description

Technical Field

[0001] This invention belongs to the field of drag-and-drop linear array sheath processing technology, specifically relating to a sheath internal heat and external cold prestress relief system and method based on PLC closed-loop control. Background Technology

[0002] Towed linear arrays are the core equipment of underwater acoustic detection systems. Towed by ships, they contain dozens or even hundreds of sensors precisely spaced within, enabling long-range detection, localization, and identification of underwater targets through beamforming technology. The performance of towed linear arrays is highly dependent on the array's geometric stability—even minute deviations in the spacing and attitude of the hydrophones can directly lead to a loss of spatial gain and direction-finding accuracy.

[0003] As a key structural carrier of the towed linear array, the polyurethane sheath's structural stability and internal stress state directly determine the array's detection accuracy, signal-to-noise ratio, and service life. During molding and coiling for storage and transportation, residual prestress inevitably accumulates in the sheath, causing a decrease in its straightness and resulting in misalignment of the internal sensor array, affecting the beamforming accuracy and positioning capability of the towed linear array. Simultaneously, stress concentration areas tend to accelerate material fatigue aging, shortening its service life.

[0004] Traditionally, stress relief for sheathing has been achieved through methods such as a single hot water bath or mechanical stretching. Traditional sheathing stress relief methods often employ a single hot water bath or hot air heating, relying on heat conduction to raise the overall material temperature above the glass transition temperature, releasing stress through molecular chain thermal relaxation. However, due to the large wall thickness and length of the sheath, a significant heat gradient exists as heat is transferred from the outside to the inside or from one end to the other, resulting in uneven heating and limited stress relief effectiveness. Furthermore, simple mechanical stretching, due to the poor ductility of the cold-state material, easily causes necking deformation at the tube end.

[0005] Therefore, efficient and non-destructive prestress relief of the sheath is a necessary prerequisite for ensuring the stable performance and long-term reliability of the drag line array. Summary of the Invention

[0006] The technical problem to be solved by this invention is to address the issue that residual prestress generated during the molding, coiling, storage, and transportation of polyurethane sheaths causes a decrease in sheath straightness and affects the accuracy and positioning capability of the drag array beamforming. The invention provides a PLC closed-loop control-based system and method for eliminating residual prestress generated during the molding, coiling, storage, and transportation of polyurethane sheaths.

[0007] The technical solution of this invention is to provide a prestress relief system for internal heat and external cold in a sheath based on PLC closed-loop control, comprising:

[0008] The sealed connection assembly is connected to both ends of the sheath to be treated, and is used to seal both ends of the sheath and provide an interface for the circulation of the internal medium;

[0009] A load-bearing rope is disposed outside the sheath, with its two ends connected to the closed connection assemblies at both ends of the sheath. When tensioned, the load-bearing rope is used to withstand axial tension.

[0010] The high-temperature circulation module is used to circulate and supply heated liquid medium into the sheath, so that the inner wall of the sheath is heated to a preset temperature.

[0011] The low-temperature spray module includes a spray ring, which is fitted outside the sheath and is used to spray and cool the outer wall of the sheath, so that the temperature of the outer wall of the sheath is lower than that of the inner wall of the sheath, and to establish a radial temperature difference in the direction of the sheath wall thickness.

[0012] Servo tension module, used to apply axial tension to the sheath;

[0013] The central control module includes a PLC controller and a host computer. The PLC controller is connected to the high-temperature circulation module, the low-temperature spray module, and the servo tension module, respectively, and is used to perform closed-loop control of the high-temperature circulation module, the low-temperature spray module, and the servo tension module based on sensor feedback data.

[0014] This invention establishes an internal heat and external cold co-processing system. By circulating hot water internally and spraying cooling water externally, a controllable temperature difference is established in the wall thickness direction. Thermal stress is used to actively offset residual stress. Combined with gradual tension loading and closed-loop control, and with the help of a PLC and host computer, the temperature, tension, flow rate and other parameters in the entire stress elimination process are monitored and coupled in real time to achieve efficient, uniform and residue-free prestress elimination.

[0015] Preferably, the sealing connection assembly includes a first plug and a last plug, which are respectively connected to the two ends of the sheath to be treated.

[0016] Preferably, the high-temperature circulation module includes a hot water tank, an electric heater installed in the hot water tank, and a water pump connected between the hot water tank and the inside of the sheath. The water pump is connected to both ends of the sheath through a hot water inlet pipe and a hot water outlet pipe, respectively, to drive the heated liquid medium to circulate inside the sheath.

[0017] Preferably, the low-temperature spray module further includes a cold water tank, the spray ring is connected to the cold water tank, the spray ring is a split-type Huff structure, and the spray head inside the spray ring is set to provide 360-degree circumferential full coverage.

[0018] Preferably, the servo tension module includes a motor, a driver connected to the motor, a guide wheel connected to the output end of the motor, and a tension sensor disposed on the load-bearing rope, for converting the rotational torque of the motor into axial tension on the sheath through the guide wheel.

[0019] Preferably, the PLC controller is connected to a temperature sensor installed inside the sheath and an infrared thermometer for monitoring the temperature of the outer wall of the sheath, and is used to adjust the heating power of the high-temperature circulation module according to the feedback signal of the temperature sensor, and to control the start and stop of the low-temperature spray module according to the feedback signal of the infrared thermometer.

[0020] Preferably, the high-temperature circulation module and the low-temperature spray module are configured to: keep hot water circulating inside the sheath at all times, and spray cooling water intermittently for 2-3 minutes each time.

[0021] This invention also provides a method for eliminating internal heat and external cold prestress in a sheath based on PLC closed-loop control, employing the above system and including the following steps:

[0022] In the high-temperature circulation step, heated liquid medium is circulated into the sheath through the high-temperature circulation module, so that the inner wall of the sheath is heated to the preset temperature.

[0023] The low-temperature spraying step involves spraying and cooling the outer wall of the sheath using a low-temperature spraying module, making the temperature of the outer wall of the sheath lower than that of the inner wall of the sheath, thus establishing a radial temperature difference in the direction of the sheath wall thickness.

[0024] The servo tension loading step applies axial tension to the sheath via the servo tension module;

[0025] The closed-loop control process involves real-time adjustment and control of the high-temperature circulation module, the low-temperature spray module, and the servo tension module based on sensor feedback data via a PLC controller and a host computer.

[0026] Preferably, in the high-temperature cycling step, the temperature of the heated liquid medium is controlled at 60-70°C.

[0027] Furthermore, in the closed-loop control step, the PLC controller dynamically adjusts the motor torque of the servo tension module according to the feedback signal of the tension sensor, adjusts the heating power of the high-temperature circulation module according to the feedback signal of the internal temperature sensor of the sheath, and controls the start and stop of the low-temperature spray module according to the feedback signal of the outer wall temperature of the sheath.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] (1) The present invention adopts a combination of hot water internal circulation and cooling water external spraying to establish a controllable radial temperature difference in the direction of sheath wall thickness. Through the dual effects of active thermal stress offsetting and molecular chain relaxation, combined with gradual tension loading and closed-loop control, the stress elimination effect is achieved, which significantly improves the straightness of the sheath and its reliability.

[0030] (2) Closed-loop heating reduces transmission loss, multi-point sensing and closed-loop regulation can accurately reflect temperature changes and make dynamic adjustments, and the closed-loop data of the whole process provides a reliable basis for quality traceability, which significantly improves the consistency of processing and the level of automation.

[0031] (3) The present invention integrates data from the servo tension module, the high temperature circulation module and the low temperature spray module through the central control module, thereby enabling real-time data monitoring and control of the entire system. The process is highly visualized, highly precise and effective. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the prestress relief system for the sheath of the present invention.

[0033] Figure 2 This is a block diagram illustrating the control principle of the sheath prestress relief system of the present invention. Detailed Implementation

[0034] The present invention will be further described below with reference to the accompanying drawings and specific embodiments:

[0035] refer to Figure 1 The prestress relief system for inner heat and outer cold of the sheath based on PLC closed-loop control of the present invention mainly includes the following structural components: sheath 1, first plug 2, tail plug 3, lifting eye screw 4, load-bearing rope 5, tension sensor 6, guide wheel 7, motor 8, driver 9, water pump 10, hot water tank 11, electric heater 12, cold water tank 13, spray ring 14, hot water inlet pipe 15, hot water extraction pipe 16, cold water extraction pipe 17, and hot water outlet pipe 18.

[0036] In this embodiment, the sheath 1, with both ends cut flat, is connected to the first plug 2 and the last plug 3, respectively. The left side is the air inlet, and the right side is the air outlet. The hot water inlet pipe 15 is connected to the first plug 2 by a thread. Two temperature sensors are installed inside the sheath near the first plug 2 and the last plug 3, and are connected to the PLC controller via data cables.

[0037] A load-bearing rope 5 is disposed on the outside of the sheath 1, with its two ends connected to the first plug 2 and the last plug 3, respectively. When tensioned, the load-bearing rope is used to withstand axial tension. The load-bearing rope 5 possesses a certain tensile strength. In this embodiment, the outer end faces of the first plug 2 and the last plug 3 are respectively provided with eye bolts for connecting the load-bearing rope 5. The eye bolts are fixedly disposed on their corresponding outer end faces and extend outward along the axial direction of the sheath. The two ends of the load-bearing rope 5 are respectively threaded and fixed in the corresponding eye bolt holes.

[0038] The guide wheel 7 possesses a certain structural strength and is designed to prevent slippage. A polyurethane coating layer is added to the surface of the guide wheel 7. Through the integrated design of the polyurethane coating layer and the guide wheel bracket, not only is the friction with the load-bearing rope increased, but wear on the load-bearing rope 5 is also reduced.

[0039] Motor 8 and driver 9 are selected as servo motors and their corresponding servo drivers, respectively. Servo motors have significant advantages in high-precision control, response speed, and stability. They are selected to operate in torque mode, enabling high-precision dynamic tension control by receiving real-time commands from the PLC controller and feedback from the force sensor.

[0040] Pump 10 should be selected as a pump with pressure resistance and high temperature resistance, with the pump body material being stainless steel or cast iron and using a mechanical seal.

[0041] The hot water tank 11 is selected with a certain capacity to ensure the system's circulating water volume and provide buffer capacity; the tank body is made of metal, which is corrosion resistant; and an external insulation layer is set to reduce heat loss.

[0042] The electric heater 12 is equipped with a fast heating element made of stainless steel to avoid contamination, and has a graded adjustment function for precise temperature control.

[0043] The cold water tank 13 is also a sealed tank with a certain capacity. The tank is made of metal, which is corrosion resistant. The tank contains a cold water pump to overcome pipeline resistance and adjusts the spray intensity through frequency conversion control.

[0044] The spray ring 14 is made of corrosion-resistant material, such as stainless steel or galvanized steel. The spray ring features a split-type design for easy installation and disassembly. The spray heads inside the ring provide 360-degree circumferential coverage and are solid conical nozzles. By controlling the water flow, uniform atomization is achieved, preventing water film slippage.

[0045] The hot water inlet pipe 15, hot water outlet pipe 16, cold water outlet pipe 17, and hot water outlet pipe 18 are made of corrosion-resistant and pressure-resistant materials, such as stainless steel or galvanized steel pipes. A certain thickness of rubber and plastic sponge insulation layer is attached to the outer wall of the pipes to reduce heat loss.

[0046] In this embodiment, a servo tension module consisting of a motor 8 and a driver 9, combined with a guide wheel 7, converts the rotational torque provided by the motor 8 into axial tension on the sheath 1. Through the high-precision positioning of the servo tension module and data feedback from the tension sensor 6, the sheath 1 can be adjusted in real time via a PLC controller according to its softening condition.

[0047] A high-temperature circulation module consisting of a water pump 10, a hot water tank 11, and an electric heater 12 drives the continuous circulation of hot water inside the sheath, maintaining a constant water temperature of 70℃ to soften the sheath. Temperature sensors placed on the inner wall of the hot water tank 11, along with two temperature sensors at the beginning and end of the sheath, are connected to a PLC controller and an HMI (Host and Controller Interface) for real-time temperature monitoring and adjustment.

[0048] In this embodiment, a low-temperature spray module consisting of a cold water tank 13 and a spray ring 14 is used to uniformly spray and cool the outer wall of the sheath. The temperature of the outer wall of the sheath can be monitored in real time by an infrared thermometer to determine the start and stop of the spray.

[0049] By combining a high-temperature circulation module with a low-temperature spray module, a hot-cold alternation scheme is achieved, allowing for different internal and external temperatures. Throughout the process, hot water is constantly circulating inside the sheath, while cold water is sprayed intermittently, only activated when a temperature difference is needed, with each spray lasting 2-3 minutes. This creates a radial temperature gradient by generating a thermal stress field opposite to the direction of the residual stress in the coil, thus counteracting the residual stress. Furthermore, the temperature of the inner wall of the sheath must be maintained higher than that of the outer wall during the process. If the internal hot water supply is stopped, the inner wall temperature drops rapidly, the temperature gradient reverses or disappears, and the thermal stress also disappears or reverses.

[0050] After the system completes its processing, the internal cleaning of the sheath is performed using a mechanical wiping method with sponge balls and a traction rope. Multiple absorbent cotton balls are placed at one end of the sheath, and the traction rope is pulled out at a uniform speed. The sponge expands and adheres tightly to the inner wall, absorbing any residual water film. For longer sheaths, multiple wiping sessions are used to ensure no blind spots are missed.

[0051] In this embodiment, the torque of the servo motor is dynamically adjusted based on feedback from the tension sensor 6. The heating power of the electric heater 12 is adjusted in segments according to the temperature sensor data of the inner wall of the hot water tank 11 to ensure that the sheath completes stress release under the condition of 60-70℃. At the same time, the start and stop of the low temperature spray module are determined based on the temperature feedback of the outer wall of the sheath. The central control module integrates and processes the data from the servo tension module, the high temperature circulation module, and the low temperature spray module. That is, the temperature and tension data are respectively connected to the PLC controller. With the help of the HMI host computer, the real-time monitoring function of the data and the parameter setting (such as tension value, inner wall temperature, outer wall temperature, data storage and traceability, etc.) adjustment function can be realized.

[0052] The system operation process of this invention is as follows:

[0053] After the two ends of the sheath to be treated are cut flat, the first and last plugs are connected respectively. The load-bearing rope is connected to the two plugs and then passes around the guide wheel and through the tension sensor. The high-temperature circulation module is activated. The electric heater heats the liquid medium in the hot water tank. The water pump drives the heated liquid medium to enter the sheath through the hot water inlet pipe and return to the hot water tank through the hot water outlet pipe, forming a closed loop, heating the inner wall of the sheath to 60-70℃. The servo tension module is activated. The servo motor works in torque mode, converting the rotational torque into axial tension on the sheath through the guide wheel. The tension sensor detects the tension value in real time and feeds it back to the PLC controller. The PLC controller dynamically adjusts the motor torque according to the feedback signal. When a radial temperature difference is required, the low-temperature spray module is activated. The cooling medium in the cold water tank sprays the outer wall of the sheath through the spray ring to cool it. The spraying continues for 2-3 minutes and then stops, keeping the temperature of the inner wall of the sheath higher than that of the outer wall, establishing a radial temperature gradient in the thickness direction of the sheath wall, and actively offsetting residual stress through thermal stress. Throughout the process, the PLC controller adjusts the heating power of the electric heater based on feedback signals from temperature sensors at both ends of the sheath, and controls the start and stop of the low-temperature spray module based on the outer wall temperature signal from the infrared thermometer. The host computer monitors and records process parameters such as tension value, inner wall temperature, and outer wall temperature in real time. After processing, a mechanical wiping method using sponge balls and traction ropes is used to clean the inside of the sheath.

[0054] Furthermore, the following combination Figure 2 The method described in this invention will be described in detail below:

[0055] The polyurethane sheath 1, with both ends cut flat, is connected to the first plug 2 and the last plug 3 respectively. The load-bearing rope 5 is connected to both plugs, passing around the guide wheel 7 and through the tension sensor 6. Process parameters are set via the HMI host computer. The high-temperature circulation module is started, and the electric heater 12 heats the liquid medium in the hot water tank 11. When the temperature sensor on the inner wall of the hot water tank 11 detects that the set temperature has been reached, the PLC controller starts the water pump 10, driving the heated liquid medium into the sheath 1 through the hot water inlet pipe 15 and back into the hot water tank 11 through the hot water outlet pipe 16, forming a closed loop to heat the inner wall of the sheath 1. Two temperature sensors inside the sheath 1, near the first plug 2 and the last plug 3, detect the internal water temperature in real time and feed it back to the PLC controller. The PLC controller adjusts the heating power of the electric heater 12 according to the feedback signal to maintain the temperature of the inner wall of the sheath within the set range.

[0056] Continuous heating cycles raise the inner wall material of the sheath 1 above its glass transition temperature, enabling the molecular chains to become mobile. The residual prestress within the material begins to be released through thermal relaxation of the molecular chains. The PLC controller sends torque commands to the servo driver, and the servo motor starts in torque mode, converting the rotational torque into axial tension on the sheath 1 via the guide wheel 7. The tension sensor 6 detects the tension value on the load-bearing rope 5 in real time and feeds it back to the PLC controller. The PLC controller controls the servo motor to output torque according to preset process parameters, applying a gradual axial tension to the sheath 1. During the gradual tension loading process, the sheath 1 undergoes slight axial stretching under the axial tension, further promoting the rearrangement of molecular chains along the stretching direction and accelerating the elimination of residual prestress.

[0057] Once the inner wall temperature of the sheath 1 stabilizes, the PLC controller activates the low-temperature spray module according to the preset process logic. The cooling medium in the cold water tank 13 sprays the outer wall of the sheath 1 with a 360-degree circumferential full coverage cooling effect through the spray ring 14, stopping after each spraying session lasting 2-3 minutes. An infrared thermometer monitors the outer wall temperature of the sheath 1 in real time. This radial temperature difference generates a thermal stress field in the thickness direction of the sheath wall. By maintaining the inner wall temperature higher than the outer wall, the inner wall's expansion tendency is greater than that of the outer wall, resulting in a thermal stress distribution in the thickness direction where the inner wall is under compression and the outer wall is under tension. This thermal stress direction is opposite to the direction of the residual prestress, achieving active cancellation. The thermal stress and the tensile stress generated by the axial tension form a stress superposition, and the molecular chains are accelerated to rearrange under the synergistic effect of axial tension and radial temperature difference, gradually eliminating the residual prestress.

[0058] After the spraying is paused, the temperature of the outer wall of the sheath 1 slowly rises under ambient conditions. When the outer wall temperature rises to a certain level, the PLC controller restarts the spray ring 14 based on feedback from the infrared thermometer, initiating the next intermittent spraying cycle, with each spraying lasting 2-3 minutes. Throughout the entire process, hot water is kept circulating inside the sheath, while cold water is sprayed intermittently, creating an alternating thermal shock effect of internal heat and external cold. Each spraying cycle re-establishes a radial temperature difference in the wall thickness direction, continuously generating a thermal stress field opposite to the direction of the residual prestress.

[0059] Throughout the process, the PLC controller continuously performs closed-loop dynamic adjustments: it dynamically adjusts the output torque of the servo motor based on the feedback signal from the tension sensor 6 to ensure that the axial tension is precisely applied according to the preset process parameters; it adjusts the heating power of the electric heater 12 based on the feedback signals from two temperature sensors located near the first and last plugs 2 and 3 inside the sheath to ensure that the inner wall temperature of the sheath remains stable within the set range; and it controls the start and stop of the low-temperature spray module based on the outer wall temperature signal fed back by the infrared thermometer. The host computer records and displays process parameters such as tension value, inner wall temperature, outer wall temperature, number of sprays, and heating power in real time, forming a complete data traceability file.

[0060] After processing, shut down the high-temperature circulation module and the low-temperature spray module to relieve axial tension. A mechanical wiping method using sponge balls and a traction rope is then employed to clean the inside of the sheath: multiple absorbent cotton balls are placed at one end of the sheath, and the traction rope is pulled out at a uniform speed. The sponge expands and adheres tightly to the inner wall, absorbing any residual water film. For longer sheaths, multiple wiping sessions are used in sections to ensure no blind spots are missed.

[0061] The above embodiments fully illustrate the workflow of the sheath internal heating and external cooling prestress elimination method based on PLC closed-loop control. By establishing a controllable radial temperature difference in the sheath wall thickness direction through the internal heating and external cooling synergistic process, and utilizing the dual effects of active thermal stress offsetting and molecular chain relaxation, combined with PLC closed-loop control and gradual tension loading, the efficient, uniform and controllable elimination of residual prestress in the sheath is achieved.

[0062] The above description only illustrates preferred embodiments of the present invention and should not be construed as limiting the scope of the claims. All equivalent modifications made using this specification are included within the patent protection scope of the present invention.

Claims

1. A prestress relief system for a sheath with internal heat and external cold based on PLC closed-loop control, characterized in that, include: The sealed connection assembly is connected to both ends of the sheath to be treated, and is used to seal both ends of the sheath and provide an interface for the circulation of the internal medium; A load-bearing rope is disposed outside the sheath, with its two ends connected to the closed connection assemblies at both ends of the sheath. When tensioned, the load-bearing rope is used to withstand axial tension. The high-temperature circulation module is used to circulate and supply heated liquid medium into the sheath, so that the inner wall of the sheath is heated to a preset temperature. The low-temperature spray module includes a spray ring, which is fitted outside the sheath and is used to spray and cool the outer wall of the sheath, so that the temperature of the outer wall of the sheath is lower than that of the inner wall of the sheath, and to establish a radial temperature difference in the direction of the sheath wall thickness. Servo tension module, used to apply axial tension to the sheath; The central control module includes a PLC controller and a host computer. The PLC controller is connected to the high-temperature circulation module, the low-temperature spray module, and the servo tension module, respectively, and is used to perform closed-loop control of the high-temperature circulation module, the low-temperature spray module, and the servo tension module based on sensor feedback data.

2. The prestress relief system for inner heat and outer cold of the sheath based on PLC closed-loop control according to claim 1, characterized in that, The closed connection assembly includes a first plug and a last plug, which are respectively connected to the two ends of the sheath to be treated.

3. The prestress relief system for inner heat and outer cold of the sheath based on PLC closed-loop control according to claim 1, characterized in that, The high-temperature circulation module includes a hot water tank, an electric heater installed in the hot water tank, and a water pump connected between the hot water tank and the inside of the sheath. The water pump is connected to both ends of the sheath through a hot water inlet pipe and a hot water outlet pipe, respectively, to drive the heated liquid medium to circulate inside the sheath.

4. The prestress relief system for inner heat and outer cold of the sheath based on PLC closed-loop control according to claim 1, characterized in that, The low-temperature spray module also includes a cold water tank, and the spray ring is connected to the cold water tank. The spray ring is a split-type Huff structure, and the spray head inside the spray ring is set to provide 360-degree circumferential full coverage.

5. The prestress relief system for inner heat and outer cold of the sheath based on PLC closed-loop control according to claim 1, characterized in that, The servo tension module includes a motor, a driver connected to the motor, a guide wheel connected to the output end of the motor, and a tension sensor mounted on the load-bearing rope, used to convert the rotational torque of the motor into axial tension on the sheath through the guide wheel.

6. The prestress relief system for inner heat and outer cold sheath based on PLC closed-loop control according to claim 1, characterized in that, The PLC controller is connected to a temperature sensor installed inside the sheath and an infrared thermometer for monitoring the temperature of the outer wall of the sheath. It is used to adjust the heating power of the high-temperature circulation module according to the feedback signal of the temperature sensor and to control the start and stop of the low-temperature spray module according to the feedback signal of the infrared thermometer.

7. The prestress relief system for inner heat and outer cold of the sheath based on PLC closed-loop control according to claim 4, characterized in that, The high-temperature circulation module and the low-temperature spray module are configured to: keep hot water circulating inside the sheath, and spray cooling water intermittently for 2-3 minutes each time.

8. A method for eliminating pre-stress caused by internal heat and external cold in a sheath based on PLC closed-loop control, characterized in that, The sheath internal heat and external cold prestress relief system based on PLC closed-loop control as described in any one of claims 1 to 7 includes the following steps: In the high-temperature circulation step, heated liquid medium is circulated into the sheath through the high-temperature circulation module, so that the inner wall of the sheath is heated to the preset temperature. The low-temperature spraying step involves spraying and cooling the outer wall of the sheath using a low-temperature spraying module, making the temperature of the outer wall of the sheath lower than that of the inner wall of the sheath, thus establishing a radial temperature difference in the direction of the sheath wall thickness. The servo tension loading step applies axial tension to the sheath via the servo tension module; The closed-loop control process involves real-time adjustment and control of the high-temperature circulation module, the low-temperature spray module, and the servo tension module based on sensor feedback data via a PLC controller and a host computer.

9. The method for eliminating pre-stress caused by internal heat and external cold in a sheath based on PLC closed-loop control according to claim 8, characterized in that, In the high-temperature cycling step, the temperature of the heated liquid medium is controlled at 60-70℃.

10. The method for eliminating pre-stress caused by internal heat and external cold in a sheath based on PLC closed-loop control according to claim 9, characterized in that, In the closed-loop control step, the PLC controller dynamically adjusts the motor torque of the servo tension module according to the feedback signal of the tension sensor, adjusts the heating power of the high-temperature circulation module according to the feedback signal of the internal temperature sensor of the sheath, and controls the start and stop of the low-temperature spray module according to the feedback signal of the outer wall temperature of the sheath.

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